With drive trains of motor vehicles in parallel hybrid design, with a transmission, an internal combustion engine and an electric motor, the electric motor can be integrated at various locations in the drive train. Typically, in terms of drive technology, an electric motor is installed at the transmission input, which provides additional hybrid functions, such as starting the internal combustion engine, electromotive starting, recuperation and boosting. Another option is to, in terms of drive technology, arrange an electric motor at the transmission output. However, the transmission ratios cannot thereby be used for an electromotive drive. Furthermore, an electric motor may also be arranged within the transmission and integrated into the drive train.
With multi-gear planetary coupling transmissions, which consist of a planetary transmission with multiple interacting planetary gear sets, for the realization of the gears of the transmission, several shifting elements designed as friction clutches and friction brakes are typically present. These are able to shift the planetary transmission under load and without any interruption of the pulling force, However, it is disadvantageous that relatively high drag losses are caused by the rotating components of these frictional shifting elements. Often, an additional starting clutch or a torque converter is required for starting.
From DE 10 2012 212 257 A1 (which has not been published before this), a planetary transmission for a hybrid drive of a motor vehicle is known. With this, the planetary transmission features three coupled planetary gear sets and multiple shifting elements, with which the pulling force of the drive train can be maintained upon a change of gears driven with the internal combustion engine with the assistance of an electric motor. Thus, this transmission does not require any frictional shifting elements subject to drag losses, or synchronizations, in order to maintain pulling force during shifting operations. In terms of drive technology, the electric motor is allocated one transmission shaft or transmission component within the transmission structure. With a first planetary gear set of this transmission, the ring gear is connectable to a fixed-housing component, the planetary carrier is connected in drive terms to the ring gear of a second planetary gear set, and the sun gear is connected to the fixed-housing component. With the second planetary gear set, the planetary carrier is connected to the ring gear of a third planetary gear set, and the sun gear is coupled with a transmission input shaft. With the third planetary gear set, the planetary carrier is connected to a transmission output shaft, and the sun gear is connectable to the fixed-housing component and is connected to the ring gear of the first planetary gear set. The shifting elements of this transmission arrangement may be formed as simple positive-locking shifting claws, since the electric motor functions as a power-shifting element. The electric motor also provides the usual hybrid functions, including a starting function. For the realization of five forward gears, this transmission arrangement features three positive-locking shifting clutches and one positive-locking shifting brake. The internal combustion engine, the electric motor and the planetary gear sets are in a coaxial arrangement, whereas, in order to achieve a particularly compact structural shape, the planetary gear sets and the shifting elements may be installed at least partially in a radial internal installation space of the electric motor.
From DE 10 2007 005 438 A1, a planetary transmission with multiple planetary gear sets and multiple shifting elements for a hybrid drive of a motor vehicle are known; with this, an electric motor is in operative connection with one of the planetary gear sets, in order to support a torque applying at the planetary gear set for the realization of a transmission ratio. An internal combustion engine, an electric drive with at least one electric motor installed in the transmission along with the planetary gear sets are in a coaxial arrangement. With a fixed-housing component, the rotor of the electric motor is connected to the ring gear of the relevant planetary gear set and the stator. The ring gear is connectable to the fixed-housing component through a positive-locking shifting element. The shifting elements are formed as friction clutches and friction brakes, or as claw clutches and claw brakes, which can be actuated by means of an assigned actuator system, for example electromotively. With a corresponding controlling of the actuators of the relevant shifting elements, shifts can be carried out with the assistance of the electric motor, without any interruption of the pulling force, whereas the respective shifting elements are synchronized by the electric motor. Upon a shifting operation, the electric motor replaces the function of a frictional-locking power-shifting element, whereas its torque is led to a transmission output shaft connectable to the output of the hybrid drive train. Hybrid functions that are known, such as electric starting, recuperation and boosting, are also possible with this drive train. With three planetary gear sets and four shifting elements, two of which are formed as shifting clutches and two are formed as shifting brakes, with this transmission, a total of six forward gears and one reverse gear are usable.